The handling of gases in metallurgical equipment is described in one or more of the following U.S. Pat.: Nos. 3,799,520, 4,007,025, 4,055,331, 4,052,042, 4,123,238, 4,145,193, 4,152,123 and 4,218,241, and in commonly assigned applications Ser. No. 198,042 filed Oct. 17, 1981 now U.S. Pat. No. 4,316,727 issued Feb. 23, 1982 and Ser. No. 281,346 filed July 8, 1981 now U.S. Pat. No. 4,375,439 issued Mar. 1, 1983 and in the various publications, patents and other documents referred to or cited in the files thereof.
Generally speaking a blower or other forced-draft unit, e.g. powered by an electric motor, can be provided in communication with a hood opening at the mouth of a furnace and can have, at its downstream or upstream side, various units designed for gas purification and/or recovery of valuable components from the furnace gases before any remainder is discharged into the atmosphere at a temperature and in a composition such that environmental pollution is minimized or is stored.
Cleaing equipment utilized for this purpose can include scrubbers, cyclones, bag and electrostatic filters and various systems which chemically or by physical processes remove toxic, noxious or other undesirable components from the gas stream or recover particulates therefrom.
Reference will also be made herein to a top-blown converter, i.e. a converter which has a mouth which can be upwardly opened in an upright position of the converter and into which a lance or the like can be inserted to blow oxygen into and onto a charge within the converter in, for example, the refining of pig iron and/or scrap into steel. Such converters are described as to their structure, operation and chemistry, for example at pages 486 ff. of The Making, Shaping and Treating of Steel, United States Steel Company, Pittsburgh, Pa. (1971).
In the operation of a top-blown converter for the oxygen refining of steel, when the converter is rotated into its upright position, a hood can be lowered over the converter mouth an communicates via ducts running from the hood with a blower and a cleaning installation of the aforedescribed type for removal of dust from the converter gases and for converter gas storage or discharge.
This hood can comprise, at its lower end, a vertically shiftable closure ring which can form a part which is raised from or lowered toward the rim of the converter surrounding the mouth thereof, this ring being connected by an annular seal with the remainder of the hood, i.e. an upper portion thereof, the seal defining an annular chamber communicating with but separated from the gas passage by this upper portion of the hood and advantageously located outwardly thereof.
The passage communicates via the ducts previously mentioned with a blower and the blower can be provided, in turn, with a controller which regulates the rate at which gases are evacuated from the region of the converter mouth by the blower.
In conventional practice, the gas pressure in the duct is measured and serves as an actual value parameter to operate the controller.
Generally speaking this measuring device or the pressure-measuring location is located well downstream of the mouth of the converter and the hood, e.g. generally in a portion of the duct which can be considered the converter stack, so that the measurement is unaffected by perturbations characteristic of activity at the mouth of the converter. It will be appreciated that the region of the converter mouth is a location at which extremely high turbulence is found, spattering from the charge can occur and a wide variety of disturbances can develop.
In the past, opting for stability of measurement, the field has confined the pressure measurement to a stack region at which reasonably uniform gas flow without such perturbations could be expected.
However, the gas flow through this region includes not only primary gases, i.e. actually evolved from the converter, e.g. by reaction of oxygen with the melt, but also secondary air, i.e. air which is drawn in by the blower between the mouth of the converter and the closure ring. For the most part, the closure ring never seals hermetically against the mouth of the converter and in many cases fairly large gaps, e.g. up to 100 mm in width, may be present between this ring and the juxtaposed rim of the converter mouth. The gas air influx through this ring can amount to thousands of standard cubic meters per hour and this flow has an effect upon the measured pressure and, or course, on the need for the blower to handle the additional contribution of displaced air.
Obviously this is highly disadvantageous not only because of the disturbance to the control point but also because the air added to the evacuated primary gases can be considered a contaminate for these gases and can reduce the economic value of the stored gas, e.g. by decreasing the heat value hereof by dilution. The volume of gas, which must be stored, can also be increased in this way to an inordinate degree.